EXTREMEPUZZLE BOOKS

Extreme Sudoku 2, puzzle 30: step-by-step solution

Step through the whole solution, or skip to the hard parts. Blue digits are placed by the walkthrough; red strike-through marks a candidate being ruled out.

Puzzle
Sudoku, number 30 of 150 in Extreme Sudoku 2
Difficulty
Expert 6 (expert and beyond), from the opening third of the book
Key technique
Nice Loops/AICs
Hard steps
26 of 51 steps need an advanced or expert technique

Blue digits are placed by the walkthrough. Red strike-through marks a candidate being ruled out. Cells are named by row and column: R3C5 is row 3, column 5. Arrow keys step too.

The key technique: Nice Loops/AICs

An alternating chain of strong and weak links. Whichever end is true, the conclusion holds, so the digit at the marked cell is ruled out.

Other advanced and expert techniques in this solve: ALS-XZ (×4), W-Wing (×3), XY-Chain (×3), Finned Fish (×2), Cell Forcing Chains, WXYZ-Wing, XYZ-Wing.

Every move above the basics is listed on the sudoku techniques page, each with a one-sentence explanation and worked examples from the books.

The hard steps, in text (24 of 26)
  1. Step 4 · Nice Loops/AICs expert
    Rules out 5 from R4C2.
  2. Step 5 · Nice Loops/AICs expert
    Rules out 5 from R6C2.
  3. Step 6 · Nice Loops/AICs expert
    Rules out 5 from R9C3.
  4. Step 7 · Nice Loops/AICs expert
    Rules out 9 from R9C5.
  5. Step 8 · Nice Loops/AICs expert
    Rules out 7 from R6C4.
  6. Step 9 · Nice Loops/AICs expert
    Rules out 6 from R4C5.
  7. Step 10 · Cell Forcing Chains expert
    Rules out 7 from R7C4; 1 from R9C5.
  8. Step 11 · Finned Fish expert
    Rules out 7 from R6C7.
  9. Step 12 · W-Wing advanced
    Rules out 4 from R3C7.
  10. Step 13 · WXYZ-Wing expert
    Rules out 3 from R6C2.
  11. Step 15 · Nice Loops/AICs expert
    Rules out 5 from R1C3, R4C1.
  12. Step 16 · ALS-XZ expert
    Rules out 5 from R3C2.
  13. Step 17 · Nice Loops/AICs expert
    Rules out 3 from R1C1.
  14. Step 22 · ALS-XZ expert
    Rules out 8 from R7C2.
  15. Step 23 · Nice Loops/AICs expert
    Rules out 9 from R1C4.
  16. Step 25 · Nice Loops/AICs expert
    Rules out 9 from R1C5.
  17. Step 27 · Finned Fish expert
    Rules out 4 from R9C6.
  18. Step 28 · Nice Loops/AICs expert
    Rules out 3 from R1C5.
  19. Step 29 · ALS-XZ expert
    Rules out 2 from R9C5.
  20. Step 30 · ALS-XZ expert
    Rules out 7 from R9C5.
  21. Step 33 · W-Wing advanced
    Rules out 3 from R6C5.
  22. Step 36 · XYZ-Wing advanced
    Rules out 6 from R6C4.
  23. Step 37 · XY-Chain expert
    Rules out 6 from R4C4.
  24. Step 42 · W-Wing advanced
    Rules out 2 from R1C3.

The book

Volume two: 150 new classic 9×9 grids, none repeated from book 1, ramping from hard to brutal.

150 new puzzles. Expert and beyond. Puzzles by M. J. Bailey. Paperback, 5 × 8 in, 196 pages, £9.99 / $11.99. Every solution in the book carries a QR code to its own walkthrough, so you can check one step without seeing the whole answer.

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More step-by-step solutions: Extreme Sudoku 1 · Extreme Killer Sudoku 1 · Extreme Killer Sudoku 2 · Extreme Sudoku 3 · Extreme Killer Sudoku 3.